Refrigeration



Sept. 12, 1939. G. A. GRUBB ET AL 2,172,442

REFRIGERATION Filed July 1, 1936 2 Sheets-Sheet l 1 N VE NTORS may! M '1 m m W wua/m WATTORNEK Sept. 12, 1939. G. A. GRUBB ET AL 2 Sheets-Sheet 2 REFRIGERATION Filed July 1, 1936 68 i W f Patented Sept. 12, 1939 I 2 UNITED STATES. PATENT OFFICE REFRIGERATION Gunnar Axel Grubb and Gustav Marten Blomqvist, Stockholm, Sweden, assignors, by mesne assignments, to Servel, Inc., New York, N. Y., a corporation of Delaware Application July 1, 1936, Serial No. 88,299

Germany July 10, 1935 19 Claims. (Cl. 62-5) Our invention relates to refrigeration, and The heat-applied to the generator causes ammore particularly to a control device for refrigermonia vapor and absorption liquid in chamber i 6 ation apparatus. to pass through an opening 25' in the lower end It is an object of our invention to provide an of a small vertical conduit 26 which constitutes improved control device for modifying the opera vapor lift and conducts ammonia vapor and 5 ation of refrigeration apparatus to initiate deabsorption liquid to the upper part of the standfrosting thereof, the device being operative to pipe I8. The liberated ammonia vapor entering terminate the defrosting automatically. the stand-pipe l8 from conduit 26, as well as the Further objects and advantages of our invenammonia vapor expelled from solution in the 10 tion will become apparent from the following destand-pipe I 3 and chamber i1, flows upward 10 scription and accompanying drawings forming a through an air-cooled rectifier 21 which conpart of this specification and of which Fig. 1 denses water vapor accompanying the ammonia diagrammatically illustrates refrigeration appavapor. The water condensed in the rectifier ratus provided with a control device embodying drains back to e generator, and t ammonia our invention; Fig. 2 is a sectional view taken at vapor flows upward to an air-cooled condenser 23 5 line 2-2 of Fig. 1 illustrating the control device comprising a coil provided with a plurality of more clearly; Fig. 3 is an enlarged fragmentary heat dissipating elements or cooling fins 29. The sectional view of parts of the control device ammonia is liquefied in the condenser 28 by surshown in Fig. 2; Fig. 4 is a sectional view taken rounding cooler air which flows over the surat line 4-4 of Fig. 3; and Fig. 5 is a sectional faces of the coil and fins, and the liquefied am- 20 view taken at line 5-5 of Fig. 4. monia flows through a conduit 30 into the up- Referring to Fig. 1, we have shown our invenper section of an evaporator coil H. The contion in connection with a refrigerator cabinet It! duit 30 is U-shaped at its lower end to provide a having thermally insulated walls Ii defining a liquid seal for preventing gas from entering the storage compartment I 2 into which access may I condenser 28. 25 be had by a door 13 hinged to the front of the An inert gas, such as hydrogen, enters 'the cabinet. Within the storage compartment I2 is lower section of the evaporator coil or cooling arranged a cooling element M of refrigeration element l4 from conduit 3| in counter-flow to apparatus for maintaining the storage compartthe liquid ammonia. The ammonia evaporates ment at a desired low temperature. and diffuses into the hydrogen with consequent 30 In the present embodiment we have shown the absorption of heat from the surroundings of the invention in connection with refrigeration appaevaporator. The lower section of the evaporator ratus of a uniform pressure absorption type concoil may be arranged within a shell 32 adapted to taining an auxiliary pressure equalizing gas. The receive trays for freezing water since the am- 1 35 refrigeration apparatus comprises a generator l5 monia evaporates at a lower temperature in this 35 having a rear chamber l6 and a forward chamber section of the evaporator coil. The upper secll communicating; with an upward extending tion of the evaporator coil may be utilized for stand-pipe or separator IS. The generator concooling the storage compartment since ammonia tains a body of absorption-liquid having 'a suitevaporates at a higher temperature in this sec- 40 able refrigerant in solution therein, and, altion of the evaporator coil, a plurality of fins 33 40 though we do not wish to be limited thereto, the being provided on the upper section to increase absorption liquid and refrigerant maybe water the effective heat transfer surface. The resulting and ammonia, respectively. mixture of ammonia and hydrogen, that is, gas

The generator I! may be heated in any suitrich in ammonia, passes from the evaporator coil able manner, as by a gas burner l9, which pro- 14 through conduit 34 which communicates at 45 jects its flame into the forward end of a horiits lower end with the lower end of an absorber zontal flue 20 which extends through the gen- 35 about which is arranged a coil 36 through erator. A suitable combustible gas is delivered which a suitable cooling medium, such as water, from a source of supply through conduit 2|, corn is circulated.

5o trol valves 22 and 23 connected in series relation, Ammonia is absorbed out of the rich gas mixand conduit 24 to the burner IS. A by-pass contfire into weak absorption liquid which enters duit 25 is provided around the valves 22'and 23 the upper part of the absorber 35 through a verto maintain a pilot flame at the burner when tically extending conduit 31. The hydrogen, either one of the valves 22 or 23 shuts oil the which is practically insoluble -and*weak in ammain supply of gas to the burner. monia, passes upward from the absorber 35 55 chamber i6 of the generator.

upper part of the stand-pipe I6, as explained above, to a higher level than it is in the absorber 36, and absorption liquid weak in ammonia flows from chamber ll through an inner conduit 42 of the liquid heat exchanger and conduit 31 into the upper end of the absorber 35. A portion of conduit 31 is provided with a plurality of fins 43 to effect additional cooling of the weak absorp,- tion liquid entering the absorber 35.

In order to vary the total pressure in the refrigeration system just described with changes in air temperature, a vessel 44' for storing hydrogen is provided having one end thereof communicating through a conduit 46 with the lower end of the condenser 26, and the opposite end thereof communicating through a conduit 46' with the gas circuit. The vessel 44' and conduits 45 and 46' provide a path of flow from the condenser 26 to the gas circuit, so that any hydrogen which passes into the condenser can flow to the gas circuit and not be trapped in the condenser. Further, should the air temperature increase so that ammonia is not liquefled in the condenser, the ammonia vapor will flow through conduit 46 to displace hydrogen in the vessel 44 and force hydrogen through conduit 46 into the gas circuit. This raises the total pressure in the system so that an adequate condensing pressure results for the increased air temperature.

In order to maintain the cooling element l4 substantially at a desired temperature, an expansible fluid thermostat responsive to the temperature of the cooling element is arranged to control valve 23 and regulate the flow of gas to the burner I6. The expansible fluid thermostat contains a volatile fluid and comprises a bulb 44 secured to and in thermal contact with the shell 32 of the cooling element l4, an expansible diaphragm 46 communicating with and secured to a hollow member 46, and a conduit 41 connecting the bulb 44 and hollow member 46. The expansible diaphragm 46 and hollow member 46 are arranged to be supported within casing 41 by a resilient diaphragm 48' to which the hollow member 46 is secured. The expansible diaphragm 46 contacts stem 4! of valve which is urged toward its closed position by a resilient spring 6i. When the cooling element tends to rise above the desired temperaturethe expansible fluid thermostat causes the expansible diaphragm 46 to expand and move the valve 66 downward against the tension of spring 6| to increase the flow of gas to the burner l6; and conversely, when the cooling element 14 tends to fall below the desired temperature, the expansible fluid thermostat causes the expansible diaphragm 46 to contract and permit the valve 66 to be urged toward its closed position to decrease the flow of gas to the burner I6.. An adjustment screw 62 bearing against the resilient diaphragm 48 is provided to regulate the position of the expanslble diaphragm 46 and hence maintain the cooling element l4 at a particular desired temperature. The control valve 23 and expansible fluid thermostat asso ciated therewith, during normal operation of the refrigeration apparatus, maintain the cooling element 14 substantially at a desired temperature.

In certain instances it is desirable to modify the normal operation of the refrigeration apparatus, and this is especially true when it is desired to melt frost that has accumulated on the upper section of the cooling element l4 and the shell 32 within which the lower section thereof is arranged.

In accordance with our invention we provide a. control device, which is arranged within the storage compartment l2 and generally illustrated at 63, to modify the normal operation of the refrigeration apparatus. The control device includes a thermal element or bulb 54 which forms part of an expansible fluid thermostat for controlling the valve 22, as will be described hereinafter. The bulb 54, referring to Figs. 4 and 5, is partially embedded in a metal sleeve 55 which is rectangular in section and secured, as by welding, to the inner sides of an angle bracket 66. The bracket 56 is secured by capscrews 51 to the bottom of the shell 32 at one edge thereof and thermally insulated therefrom by a strip of insulating material 66 and ferrules 59 on the capscrews which are also formed of insulating material.

The bulb- 64, which is spaced from andout of thermal contact with the cooling element l4 due to the manner in which it is secured to the latter, is rendered operative to modify the operation of the refrigeration apparatus by means providing a heat conductive path between the bulb 54 and shell 32 when frost, indicated at 60, has accumulated on the latter. This may be effected automatically by so constructing and arranging the control device 63 that the bulb 54 is placed in thermal contact with the shell 32 upon opening the door [3 of the refrigerator cabinet It. To this end a rod 6| is provided which is movable in its length-wise direction alongside the cooling element through openings in the inwardly bent ends 62 of the bracket 66. The forward end of the rod 6| is. provided with an enlarged head 6| and intermediate the ends of the rod a helical spring 63 is disposed between a flanged member 64 fixed to the rod and a second flanged member 65 flxed to the bracket 56. When the door I3 is closed the spring 63 is compressed and the rod 6| is urged or biased forward with the head 6| bearing against the inner liner of the door. Upon opening the door l3 the rod 6|, due to the tension of spring 63, is moved forward.

A carriage or metal block 66 is slidably mounted on the rod 6| and, with a forward movement of the rod, is also moved forward by a pin 61 which is flxed to the rod at the rear of the carriage. To the carriage 66 is secured a forwardly extending leaf spring 68 the outer end of which is adapted to slide over and bear lightly against-the downwardly depending arm or plate 66 of. an inverted U-shaped part of the bracket 66. When the door I3 is opened and no frost or only a'slight' amount of frost has accumulated on. the shell 32, the carriage 66 is moved forwardby the pin 61 and the curved portion of the leaf spring 66 is spaced from and out of thermal contact with ribbed portion III of the shell 32. With such forward movement of the carriage 66 the latter slides over the top surface of the sleeve il within which is embedded the bulb 64. To insure good thermal contact between the carriage 66 and sleeve 66, a

curved leaf spring H is secured within the inverted U-shaped part of the bracket 56. Upon subsequently closing the door l3, the rod 6| is moved rearwardly and, to effect rearward movement of the carriage 66, a helical spring I2 is provided having one end secured to the carriage and the other end secured to the bent end 62 of the bracket 56. The spring 12 is weaker than spring 63 so that, when the door I3 is opened, forward movement of the rod 6| and carriage 66 is insured.

When the carriage 66 is moved forward by the rod 6| and pin 61 upon opening the door l3, and the shell is coated with a layer of frost of considerable thickness, as indicated at 60, the curved portion of leaf spring 68 contacts the frost at the ribbed portion 10 of the shell 32 and the outer end thereof frictionally engages the downwardly depending arm 69. Upon subsequently closing the door l3 the rod 6| is moved rearwardly but the carriage 66, due to the layer of frost 60, remains adjacent the ribbed portion 10 of the shell 32. With the carriage in this position, a heat conductive path between the shell 32 and bulb 54 is provided through the layer of frost 66, leaf spring 68, carriage 66 and sleeve 55 within which the bulb 54 is embedded. Due to this heat conductive path the temperature of the bulb 54 is reduced and reaches a value which is approximately that of the shell 32.

When the temperature of the bulb 54 is reduced it is effective to operate valve 22 and reduce the flow of gas to the burner l9, thereby stopping the operation of the refrigeration apparatus and per.- mitting melting of frost on the cooling element. This may be accomplished, as shown in Fig. 1, by connecting the bulb 54 to a conduit 54' which is connected at its lower end to the upper chamber 13 of valve casing 14 within which is arranged a flexible partition or diaphragm 15. The diaphragm 15 contacts the upper end of stem 15 of valve 11 which is urged to its closed position by a resilient spring I8. The bulb 54, conduit 54 and chamber 13 constitute an expansible fluid thermostat containing a volatile fluid which increases and decreases in volume with corresponding changes in temperature. During normal operation of the refrigeration apparatus when the bulb 54 is out of thermal contact with the shell 32, the volatile fluid is effective to flex the diaphragm 15 downward against the tension of spring 18 and maintain the valve 11 in its open position, so that valve 23 alone is operative to control the operation of the refrigeration apparatus in response to the temperature of the cooling element. When a layer of frost has accumulated on the shell 32 and the carriage 66 and spring 68 bridge the gap between the shell 32 and bulb 54 and the temperature of the latter is reduced, the volume of the volatile fluid will be decreased and the spring 18 effective to move the valve to its closed position to reduce the flow of gas to the burner. When the main supply of gas is shut off, a small quantity of gas flows through the by-pass 25 to maintain a pilot flame at the burner l9.

After the carriage 66 has once been moved adjacent to the ribbed portion 10 of the shell 32 and the operation of the refrigeration apparatus has been stopped, any closing and opening movements of the door I3 will not affect the defrosting of the refrigeration apparatus. Only after the layer of frost 66 has melted sufficiently to reduce the frictional engagement of the spring 68 with the arm 69 and permit spring 12 to pull the carriage rearwardly will the bulb 54 again be out of thermal contact with the shell 32. With the carriage 66 in a position to the rear of the ribbed portion 10 of the shell 32, the volatile fluid in the bulb 54, conduit 54' and chamber 13 of valve 22 will be increased in volume and effective to move the valve 11 to its open position, and the 5 refrigeration apparatus will again resume nor mal operation under the control of valve 23 and bulb 44.

In order to provide an effective heat conductive path when the carriage 66 is maintained in posi- 10 tion adjacent the ribbed portion 10 of the shell, due to a layer of frost, the carriage 66 and spring 68 are preferably formed of metal which is a good heat conductor. The carriage 66, for example, may be formed of aluminum, copper or brass, and 5 the leaf spring 68 may be formed of copper, beryllium or steel. If desired, the operation of .the control device 53 may be effected manually instead of automatically upon opening the door I3. In some instances it may not be desirable to initiate defrosting, as when immediate freezing of water is desired, and in such cases suitable locking means may be provided which will prevent forward movement of the rod 6| when the door I3 is opened. When the control device 53 is operated manually, such manual operation may be effected from outside the refrigerator cabinet ID by suitable connecting means. In order to insure frictional engagement of the spring 68 with the arm 69 of bracket 56 when a layer of frost. has accumulated on the shell 32, the latter may be provided with projections or teeth which will permit forward movement of the carriage 66 but prevent rearward movement of the carriage when the shell is coated with a layer of frost.

In View of the foregoing it will be understood that we have provided an improved control device for refrigeration apparatus and, while we have shown anddescribed a single embodiment of our invention, such variations and modifications are contemplated as fall within the true spirit and scope of our invention, as pointed out in the following claims.

What is claimed is:

1. A refrigerator comprising a cabinet having 45 a thermally insulated storage compartment provided with an opening, a door for closing the opening, refrigeration apparatus including a cooling element arranged to cool the storage compartment, a thermostat having a part spaced from said cooling element for controlling the operation of said refrigeration apparatus, and structure operable upon opening said door to provide 'a heat conductive path between said part and frost accumulated on said cooling element to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of the frost.

2. A refrigerator comprising a cabinet having a thermally insulated storage compartment prono vided with an opening, a door for closing the opening, refrigeration apparatus including a cooling element arranged to cool the storage compartment, a thermostat having a part spaced I from said cooling element for controlling the operation of said refrigeration apparatus, and structure operable upon opening said door to provide a heat conductive path between said part and frost accumulated on said cooling element to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of the frost, said structure being so constructed and arranged that the modified operation of said refrigeration apparatus is continued irrespective of subsequent closing and opening movements of said door until said cooling element is substantially defrosted.

3. A refrigerator comprising a cabinet having a thermally insulated storage compartment provided with an opening, a door for closing the opening, refrigeration apparatus including a cooling element arranged to cool the storage compartment, a thermostat having a part spaced from said cooling element for controlling the operation of said refrigeration apparatus, and structure operable upon opening said door to provide a heat conductive path between said part and frost accumulated on said cooling element to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of the frost, said structure being so constructed and arranged that the heat conductive path is broken and the modified operation of said refrigeration apparatus is terminated when said cooling element is substantially defrosted.

4. Refrigeration apparatus including a cooling element, a thermostat having a part spaced from said cooling element for controlling said .refrigeration apparatus, a metal member arranged to be supported for movement with respect to said cooling element and said part, meansfor imparting movement to said member to move the latter adjacent to a'portion of the cooling element, and structure including said member operative when the latter is positioned adjacent said portion of the cooling element to provide a heat conductive path between said part and frost accumulated on said portion to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of the frost.

5. Refrigeration apparatus including a cooling element, a thermostat having a part spaced from said cooling element for controlling said refrigeration apparatus, a metal member arranged to be supported for movement with respect to said cooling element and'said part, means for imparting movement to said member to move the latter path between said part and frost accumulated on said portion to render said thermostat capable of modifying the operaton of said refrigeration apparatus to cause melting of the frost, and means for moving said member away from said portion of the cooling element to open the heat conductive path and terminate the modified operation of said refrigeration apparatus when said cooling element is sulfitantially defrosted.

6. Refrigeration apparatus including a cooling element, a thermostat having a part spaced from 'said cooling element for controlling said refrigeration apparatus, a rod supported for lengthwise movement alongside said cooling element, a metal member movable on said rod with respect to said part, means-on said rod for imparting movement to said member to move the latter ad'- jacent to a portion of said cooling element when movement is imparted to said rod, and structure including said member 1 operative when the latter is positoned adjacent to said portion of the cooling element to provide a heat conductive path between said part and frost accumulated on said portion to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of the frost.

.7. Refrigeration apparatus including a cooling element, a thermostat having a part spaced from said cooling elementfor controlling said refrigeration apparatus, a rod supported for lengthwise movement alongside of said cooling element, a metal member movable on said rod with respect to said part, means on said rod for imparting movement to said member to move the latter adjacent to a portion of said cooling element when movement is imparted to said rod, structure including said member operative when the latter is positioned adjacent to said portion of the cooling element to provide a heat conductive path between said part and frost accumulated on said portion to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of the frost,

and means for moving said member away from said portion of the cooling element independent of any movement of said rod to open the heat conductive path and terminate the modified operation of said refrigeration apparatus when said cooling element is' substantially defrosted.

8. A refrigerator comprising a cabinet having a thermally insulated storage compartment pro-' element,means operable'upon opening said door for imparting movement to said member to move the latter adjacent to said portion of the cooling element, and structure including said member operative when the latter is positioned adjacent to said portion to provide a heat conductive path between said part and frost accumulated on said portion to render said thermostat capable of modifying the operation of said refrigeration appa ratus to cause melting of the frost.

- 9'. A refrigerator comprising a cabinet having a thermally insulated storage compartment prov.ded with an opening, a door hinged to said cabinet for closing the opening, refrigerationapparatus including a cooling element arranged within the storage compartment, a thermostat having a part arrangedadjacent to and spaced from said cooling element for controlling the operation of said refrigeration apparatus, a metal member arranged'to be supported for movement toward and away from a portion of said cooling element,-

means operable upon opening said door forimparting movement to said member to move-the latter adjaoent'to said portion of the cooling element, and structure including said member opertive when.the latter is positioned adjacent to said portion to provide a heat conductive path between said part and frost accumulated on said portion to render said thermostat capable of mod.-

iiying the operation of said refrigeration apparatus to cause melting, of the frost, said structure including resilient means carried by said member and adapted to bear against froston said porratus including a cooling element arranged within the storage compartment, a thermostat having a part arranged adjacent to and spaced from saidcooling element for controlling the operation of said refrigeration apparatus, a metal member arranged to be supported for movement toward and away from a portion of said cooling element, means operable upon opening said door for imparting movement to said member to move the latter adjacent to said portion of the cooling element, structure including said member operative when the latter is positioned adjacent to said portion to provide a heat conductive path between said part and frost accumulated on said portion to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of the frost, and means for moving said member away from said portion of the cooling element to open the heat conductive path and terminate the modified operation of said refrigeration apparatus when said cooling element is substantially defrosted.

11. Refrigeration apparatus including a cooling element, a thermostat having a part adjacent to and spaced from said cooling element for controlling said refrigeration apparatus, a metal member arranged to be supported for movement toward and away from a portion of said cooling element,a plate disposed adjacent to and spaced from' said portion of the cooling element, a curved resilient leaf spring carried by said member, means for imparting movement to said member to move the latter adjacent to said plate and said portion of the cooling element, said spring contacting frost on said portion of the cooling element and frictionally engaging said plate when sufficient frost has accumulated on said portion, and structure including said spring and said member operative when the latter is positioned adjacent to said portion of said cooling element to provide a heat conductive path between said part and the frost to render said thermostat capable of modifying the operation of saidrefrigeration apparatus to cause melting of the frost.

12. Refrigeration apparatus including a cooling element, a thermostat having a part adjacent to and spaced'from said cooling element for controlling said refrigeration apparatus, a metal member arranged to be' supported for movement toward and away from a portion of said cooling element, a plate disposed adjacent to and spaced from said portion of the cooling element, a curved resilient leaf spring carried by said member, means for imparting movement to said member to move the latter adjacent to said plate and said portion of the cooling element, said spring contacting frost on said portion of the cooling element and frictionally engaging said plate when sufficient frost has accumllated on said portion, structure including said spring and said member operative when the latter is positioned adjacent to said portion of the cooling element to provile a heat conductive path between said part and the frost to render said thermostat capable of molifying the operations of said refrigeration apparatus to cause melting of the frost, and means for moving said member away from said portion of the cooling element to open the heat conductive path and terminate the modified operation of said refrigeration apparatus when said cooling element is substantially defrosted and said spring is out of frictional engagement with said plate.

13. Absorption refrigeration apparatus including a generator and a cooling element, a burner for heating said generator, means including a conduit for conducting fuel to said burner, a

thermostat having a part thermally spaced from.

said cooling element for controlling the flow of fuel to said burner, and structure including a metal member movable with respect. to said part and operative to provide a heat conductive path between said part and frost accumulated on said cooling element to render said thermostat capable of reducing the flow of fuel to said burner to modify the operation of said refrigeration apparatus and cause melting of the frost.

to said burner to maintain said cooling element substantially at a desired temperature or temperature range, a second thermostat having a part thermally spaced from said cooling element for controlling the flow of fuel to said burner,' and structure including a metal member movable with respect to said part and operative to provide a heat conductive path between said part of the second thermostat and frost accumulated on said cooling element to render said second thermostat capable of controlling the flow of fuel normally affected by said first thermostat to modify the operation of said refrigeration apparatus and cause melting of the frost.

15. Refrigeration apparatus including a cooling element, a thermostat element spaced from said cooling element for controlling said refrigeration apparatus, said thermostat element being fixed with respect to said cooling element when frost melts on the latter, and a thermal conductive member movable with respect to said thermostat element and operative to bridge the gap between said thermostat element and frost on. said cooling element to render said thermostat element capable of modifying the operation of said refrigeration apparatus to cause melting of frost.

on said cooling element.

16. Refrigeration apparatus including a cooling element, a thermostat element thermally spaced from said cooling element, said thermostat element being fixed with respect to said cooling element when frost melts on the latter, a thermal conductive member-movable with respect to said thermostat element and adapted to be interposed between said thermostat element and said cooling element, and said thermal conductive member being so constructed and arranged that it'is retained in position between said thermostat element and frost on said cooling'ele'ment when frost has accumulated on the latter to provide a heat conductive path between frost on said cooling element and said thermostat element, whereby said thermostat element is capable of modifying the operation of said refrigeration apparatus to cause melting of frost on said cooling element.

17. Refrigeration apparatus including a cooling element, a thermostat element spaced from said,

paratus and when frost tends to accumulate on said cooling element.

18. In refrigeration apparatus including a cooling element and having a source of energy supply, and thermostatic means responsive to a temperature condition affected by said cooling element for normally controlling the energy supply,

additional thermostatic means including a part spaced from said cooling element, and structure 'thermostatic means to modify the operation of said refrigeration apparatus to cause melting of the frost.

19. Refrigeration apparatus including a cooling element, a thermostat including a part thermally spaced from said cooling element for controlling said refrigeration apparatus, and structure including a thermal conductive member movable with respect to said part and operative to provide a heat conductive path between said part and frost on said cooling element to render said thermostat capable of modifying the operation of said refrigeration apparatus to cause melting of frost on said cooling element.

GUNNAR -AXEL GRUBB. GUSTAV MAR'I'EN BLOMQVIST. 

